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更新时间:2017-6-5 18:40:07 来源:纽约时报中文网 作者:佚名

A New Formula to Help Tame China’s Yellow River

Each year thousands of tourists flock to a reservoir along the Yellow River in China to witness a ritual cleansing so violent that it can look as if the earth just exploded. At the end of June and the start of July, for as long as two weeks before the flood season, Chinese officials open large portals along the walls of the Xiaolangdi Dam, releasing clear and muddy water simultaneously from the reservoir above to the river below. It gushes out, and in some years clouds the color of doom ascend beyond the dam’s walls.


The Yellow River is considered the cradle of China’s civilization — but also its sorrow. Its vast floodplains coaxed people in for agriculture. Yet its violent floods have killed millions.


The precautionary purging at the Xiaolangdi Dam, which has occurred annually since 2002, is the latest high-tech attempt to prevent flooding and tame the Yellow River, which today threatens more than 80 million people. It carries sediment more concentrated than in any other river in the world — so much that tiny particles of sand and silt clog reservoirs, raise riverbeds, break levees and cause potentially catastrophic floods. During what is called the Water and Sediment Regulation Discharge Project at Xiaolangdi Dam, muddy water evacuates sediment from the reservoir, and clear water washes sand out from the channel below to reduce flood risk.


The annual purge can lower the riverbed by about six feet a year on average, but a surprising discovery about the river’s bottom, as well as its unusual capacity to carry high loads of sediment, could one day mean that the purge may not be as effective at preventing floods. In a study published last month in the journal Science Advances, researchers suggest new considerations to take into account when conducting this yearly event.

泄洪能把河床平均每年降低约六英尺,但是一项关于河底的意外发现,以及黄河运送大量沉积物的不寻常能力,可能意味着将来有一天,这种泄洪方式在防洪方面不会产生同样的效果。在上个月《科学前沿》(Science Advances)杂志发表的一项研究中,研究人员建议在今年的泄洪工作中,将一些新的因素考虑在内。

Previous models couldn’t explain how the Yellow River transports about a billion tons of sediment thousands of miles to the sea each year. Compared with the Mississippi River, it holds three times as much sediment and just a tenth of the water. But Hongbo Ma and Jeffrey A. Nittrouer, both geologists at Rice University and lead authors of the study, examined historical data and scanned the bed of the river with 3-D sonar.

之前的模型不能解释黄河如何每年携带约10亿吨沉积物,奔流数千英里,运到海里。黄河运送的沉积物量是密西西比河的三倍,而运送的水量仅为它的十分之一。不过,赖斯大学(Rice University)的地质学家、这项研究的主要作者马宏博和杰弗里·A·尼特劳尔(Jeffrey A. Nittrouer)研究了历史数据,用3D声纳设备扫描了黄河河床。

“It was very striking to see that the Yellow River bottom is basically flat,” Dr. Ma said.


It was assumed that the river’s flow produced relatively tall, closely spaced dunes that slowed the water and sucked up energy that might otherwise be available for sediment transport. But the Yellow River, with its fine sediment particles, had low dunes spaced far apart, freeing more energy to move the sediment.


With this discovery, the researchers and their colleagues developed a universal formula that could be used on all kinds of rivers to predict the exact sediment amounts traveling in the fluid. They can better predict where and when floods will occur or new land will be formed.


“We want to make the Yellow River the poster child of rivers and deltas around the world,” Dr. Nittrouer said.


At the Xiaolangdi Dam, competing systems may simultaneously lower the riverbed as clear water flushes away sediment and raise it as sandy water forms dunes that slow the sediment flow. Combining the new formula with the old model could help operators prevent more floods by achieving a better balance between the systems.


Last year, officials unexpectedly canceled the release because there wasn’t enough water or muck to need flushing, possibly because of lighter rainfall.


To not disappoint tourists, they released clear water from the dam for just 15 minutes.


It’s unclear what to expect this year. “It would have to be the end of June or July,” Dr. Ma said, “but honestly we’re not aware of whether this event will happen or not.”